1. Field of the Invention
The invention relates to a thermostatic device having two operating thresholds so as to provide two regulating ranges which can be selectively activated.
Such devices are useful especially in the field of motor vehicles, for the purpose of optimizing the cooling of the vehicle""s engine depending on the load on it.
2. Description of Related Art
Conventionally, the liquid cooling circuit for internal combustion engines comprises a system of hoses connecting the engine to a cooling radiator into which a thermostatic device is inserted. The thermostatic device modifying, in the liquid intended for the engine, the proportion of so-called xe2x80x9ccoldxe2x80x9d liquid coming from the radiator to the so-called xe2x80x9chotxe2x80x9d liquid which has not passed through the latter, so as to deliver to the engine block coolant at the same, in principle optimized, temperature whatever the circumstances.
However, it has proved to be the case that the engine, when under a very high load, xe2x80x9cheats upxe2x80x9d to such an extent that maintaining the normally optimal temperature at the inlet of the engine leads to an internal engine temperature likely to damage it.
In order to avoid this drawback, it is known to choose as the liquid injection temperature a lower temperature than the normally optimal temperature, and thus at a low load, which corresponds to the case in which a vehicle is used most often, the engine operates appreciably below the optimal value and the fuel consumption and pollution are increased.
For the purpose of remedying this new drawback, the subject-matter of document FR 93/11 919 relates to a thermostatic device having a single thermostatic element, which regulates the temperature by means of a valve and shifts the regulating range only when the engine is operating under full load, in order then to regulate it at a lower temperature than the optimal temperature under normal conditions, generally approximately at half load. For this purpose, the thermostatic element includes an electrical heating member providing it with additional heating when a suitably placed probe detects that the engine is operating near its full load. However, should the system for electrically heating the element fail, the situation always returns to the high-temperature regulation corresponding to the half load, which carries risks of damaging the engine when it is operating at full load. Furthermore, should the thermostatic element itself fail, it no longer fulfils its regulating function and the regulating valve remains closed, which very rapidly leads to engine damage.
Again for the purpose of alleviating this drawback, the subject-matter of document FR 85/15 967 and that of U.S. Pat. No. 4,875,437 relate to a thermostatic device comprising a regulating element placed in the cooling circuit and a heated offsetting element which is placed outside the cooling circuit. By means of this design, even if the heated offsetting element itself should fail, a regulating action remains, but this regulating is at a high temperature, which means that risks of damaging the engine when the latter is operating at full load remain.
It is an object of the present invention to alleviate these drawbacks and for this purpose the subject of the present invention is a thermostatic device having two regulating conditions. The thermostatic device comprising a moveable fluid-metering component which includes two valves and is designed to move in a chamber having a first, fluid inlet, port, a second, fluid outlet, port and at least one third port. At least two of these three ports are surrounded by respective seats in the case of the two valves so that when any one of the valves leaves its seat and moves away therefrom, the other one moves towards its own seat possibly as far as closure. The moveable metering component is carried by one part of a thermostatic fluid-metering element which can move with respect to another part of the thermostatic element, which part is arranged at least partially outside the chamber. The device is characterized in that it comprises a casing part in the form of a pipe, one end of which enters the chamber via a valve seat surrounding one of the ports of the chamber. The pipe contains a thermostatic threshold-setting element having a moveable part carrying a moveable threshold-setting component provided with a moveable stop in the case of that part of the thermostatic metering element which is outside the chamber. Also, the thermostatic threshold-setting element has electrical heating means suitable for being electrically connected to an electrical power supply that can be selectively activated and deactivated so that, when the setting element is not heated, the distance between the moveable stop and the port seat on the side facing the pipe, and thus the temperature for which this seat is released by its valve, are less than when it is heated.
Thus, in the event of a mechanical or electrical failure (including a failure of the control electronics) other than complete destruction of the device, in the absence of any additional expansion of the threshold-setting element, the device always regulates, not at a high temperature, but at a low temperature.
The device may also have one or more of the following features:
1) the pipe is centered on a longitudinal axis, on which the two valve seats are also centered, and the moveable part of the thermostatic element which carries the moveable component comprising the two valves can move in longitudinal translation along this axis;
2) the moveable component of the thermostatic threshold-setting element has a stationary part housed in a socket inside the pipe and connected to the wall of the latter, and a moveable part having a free end turned towards one end of the pipe, which is on the opposite side of the seat for the pipe;
3) the moveable component of the thermostatic threshold-setting element comprises a yoke-shaped compensator extending in the direction of the seat of the pipe, and the moveable stop is carried by this moveable component at the ends of arms of the yoke, which are located on the same side as the frustoconical seat;
4) the electrical heating means comprise a resistance heating element housed in a stationary part of the thermostatic threshold-setting element, the fixed part being carried by a socket inside the pipe;
5) the electrical heating means are connected by electrical conductors to an electrical power supply, which is also connected to a temperature detection probe suitable for detecting the temperature of a liquid;
6) the electrical heating means are connected by electrical conductors to an electrical power supply, which is also connected to a temperature detection probe suitable for detecting the temperature of a liquid and to an alarm, so that, when the probe detects a temperature at least equal to a predetermined safety temperature, the electrical power supply is deactivated and thus, on the one hand, the setting element is not electrically heated and the device regulates within a low temperature range and, on the other hand, the alarm is activated;
7) the chamber includes an outlet port surrounded by a seat made in the pipe for a valve, an outlet port surrounded by a seat for a valve, and an inlet port;
8) the inlet port is an inlet port for hot liquid coming from an engine, for example of a vehicle, and the outlet ports are outlet ports for hot liquid which are suitable for being connected, respectively, to an inlet of a cooling radiator and to an inlet of the engine possibly via a circulating pump;
9) the chamber has an inlet port surrounded by a seat made in the pipe for a valve, an inlet port surrounded by a seat for a valve, and an outlet port;
10) the inlet port surrounded by a seat made in the pipe is an inlet port for cold liquid, suitable for being connected to a cooling radiator, for example of a vehicle, the other inlet port is an inlet port for hot liquid coming from an engine of the vehicle, and the outlet port is an outlet port for hot liquid or for cold liquid or for a mixture of hot liquid and cold liquid, depending on the position of the thermostatic metering element.